Oval Port Big-Block Chevy Cylinder Heads - The Big O

The best way to illustrate the power potential of performance cylinder heads is on the dyno.

The heads from Dart and Procomp Electronics were as-cast with no additional machining of any kind. Heads supplied by Brodix and Trick Flow Specialties both featured port matching, but the Brodix head carried it one step further with CNC work on the combustion chamber. The AFR, Edelbrock, and 049 heads from Dr. Js all combined full porting and chamber work.

As expected, the level of work applied to the heads resulted in differences in flow and power. Take note that the combustion chamber volumes varied from 110 cc to 121 cc, resulting in a difference in static compression of 1 full point. This alone was worth 3-4 percent in power, so bear this in mind when reviewing the results.

The one upgrade we would like to see on many of the heads is more valve spring pressure. At the top of the power curve, some suffered slightly due to inadequate spring pressure.

Power and price usually go hand in hand, but check out the retail prices to determine how your favorite does in the all-important bang-for-the-buck category. Next month, we'll be testing some popular rectangular port heads on a larger-displacement Rat.

Test 1: Chevy Peanut-Port Heads

2/32

Our intention was to run a set of stock peanut-port heads and a set of stock oval-port heads, but our oval-port heads fell through. The stock peanut-port heads featured a 2.06/1.72 valve combination with 118cc combustion chambers. Closer inspection revealed that even our "stock" peanut-port heads had been milled sometime in their long life. The small valves, port volume, and flow numbers made them less than ideal with this healthy hydraulic roller cam, but they surprised us by exceeding 500 hp with peak numbers of 512 hp and 514 lb-ft of torque. Looking at the graphs, the peanut-port heads actually ran neck and neck with the aftermarket heads up to 4,500 rpm, which makes them ideal for intended low-speed truck applications. With a little porting, they make good heads for a mild street BBC, especially a small-displacement 396.

Notes: Out-of-the box 360 castings

Retail Price- N/A

Intake Valve Size-2.06

Exhaust Valve Size-1.72

Intake port vol-253 cc

Chamber Volume-117 cc [milled]

Peak Power-512 @ 5,800 rpm

Peak Torque-514 lb-ft @ 4,800 rpm

Avg HP [3,500-6,300]-453.4 hp

Avg TQ [3,000-6,500]-489.9 lb-ft

Tq @ 4,000 RPM-508.5 lb-ft

Flow Data: CFM @ 28-ins

Lift

In

EX

.050

33

24

.100

57

51

.200

117

94

.300

185

128

.400

233

158

.500

247

179

.600

250

297

.700

250

211

3/32

Test 2: Airflow Research 265

4/32

The AFR 265 heads didnt produce the highest peak power and torque numbers of the test because of peak flow numbers. In fact, every aftermarket head we tested actually offered better flow number numbers at 0.700 lift (and many at 0.600 lift) than the AFRs. Even the ported 049 heads outflowed the AFRs at 0.700 lift, but our 0.580-lift cam never made it to 0.700 lift. Besides, power doesnt come from peak flow, it comes from maximizing flow in the usable lift range. Since the valve must open up to the maximum lift value, then close down, it spends twice as much time in the rest of the lift range as it does at the peak. Using the additional mid-lift flow offered by the AFR 265s, the 468 BBC produced 613 hp and 559 lb-ft of torque. The spring package provided by AFR allowed the hydraulic roller motor to rev cleanly to 6,500 rpm. In terms of average power production from 3,500 rpm to 6,300 rpm, the AFR 265s produced 501 hp and 536 lb-ft of torque, while knocking down 520 lb-ft at 4,000 rpm.

Notes: Fully ported, chambers worked

Retail Price- $2,238

Intake Valve Size-2.19

Exhaust Valve Size-1.88

Intake port vol-266 cc

Chamber Volume-112 cc

Peak Power-612 hp @ 6,400 rpm

Peak Torque-559 lb-ft @ 5,300 rpm

Avg HP [3,500-6,500]-501 hp

Avg TQ [3,500-6,500]-536 lb-ft

Tq @ 4,000 RPM-520.3 lb-ft

Flow Data: CFM @ 28-ins

Lift

In

EX

.050

37

30

.100

73

63

.200

164

141

.300

241

196

.400

298

239

.500

332

260

.600

331

273

.700

316

280

5/32

Test 3: Brodix Race Rite Oval 270

6/32

The Brodix Race Rite oval-port heads featured 270cc intake ports that flowed just shy of 340 cfm--enough to support nearly 700 hp on the right application. Obviously, our mild combination could not take full advantage of what the Brodix heads had to offer, but they performed exceptionally well on the 468 nonetheless. Unlike the AFR or Edelbrock offerings, the Brodix Race Rite heads relied on CNC porting only in the combustion chamber. The intake ports received a minor gasket match, but the cutter was not allowed to do any serious work. The lack of CNC porting didnt seem to hurt the flow rates, as the intake and exhaust ports of the Brodix heads flowed 336 cfm and 270 cfm, respectively. This allowed the Brodix-headed 468 to produce 591 hp and 553 lb-ft of torque. The BBC averaged 492 hp and 528 lb-ft of torque while thumping out 512.8 lb-ft at 4,000 rpm.

9 Our test motor featured a forged crank and rods from Procomp Electronics and forged pistons from Probe Racing. The 18cc domed pistons produced a static compression ratio over 10.0:1 with the smallest chamber heads.

10 ARP supplied the necessary head studs and bolts, while we relied on Fel Pro head and intake gaskets during the test.

11 To properly test the heads, Comp Cams came through with an XR300HR hydraulic roller cam and lifters for our test motor. The XR300HR cam offered a 0.560/0.580 lift split, a 248/254 duration split, and a 110-degree LSA.

14 Fire for our fuel was supplied by an MSD billet distributor and Digital 7 ignition amplifier. Timing was adjusted to maximize power, but most heads ran best near 40 degrees of total timing.

15 Prior to the dyno test, each head was run on the flow bench to determine not only peak flow numbers, but flow through the entire lift range.

16 The intake ports and combustion chamber volumes were also verified. The port volumes for the various heads varied by over 45 cc, while the chamber volumes varied by as much as 11 cc.

17 It was also necessary to mock up each head to determine pushrod and ARP head bolt/stud lengths. Spring pressure was also a critical issue, as insufficient pressure limited available engine speed. Despite what manufacturers tell you, BBC heads need between 180-200 pounds of seat pressure and near 400 pounds of open pressure when running a hydraulic roller cam.

18 It was necessary to adjust the valves after each head/pushrod swap. The hydraulic roller cam made valve adjustment a snap.

19 The stock valve springs on the peanut-port heads were obviously not going to get the job done with our hot hydraulic roller cam, so they were upgraded to a set of 26120 beehive springs from Comp Cams. Comp sold the entire upgrade, including the 0.300-thick rotator eliminator spring cups.

20 The heads run in the test varied greatly with some offering as-cast combustion chambers.

21 A couple of the manufacturers opted to supply CNC'd combustion chambers. The chamber volume varied from a low of 110 cc to a high of 121 cc.

COMMENTS

related articles

402 Big Block Cylinder Head Swap - Big or small, an engine without a flow is nothing short of a large hunk of metal that shudders and trembles. An engine that has flow will be your best friend. - Super Chevy Magazine » Read More

For this build up, we decided to go big on the performance side with an oval port big-block engine. What is big for a street engine? How does 800 hp sound? Eight hundred horsepower constitutes serious power in anyone’s book, but making power is rarely a problem. » Read More